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          <h1 class="post-title" itemprop="name headline">decorator修饰器语法</h1>
        

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        <h1 id="什么是decorator"><a href="#什么是decorator" class="headerlink" title="什么是decorator"></a>什么是decorator</h1><ul>
<li>Decorator是在声明阶段实现类与类成员注解的一种语法</li>
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<figure class="highlight coffeescript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">@log</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Numberic</span> &#123;</span></span><br><span class="line">     @readonly PI = Math.PI;</span><br><span class="line">      </span><br><span class="line">     @validate</span><br><span class="line">     add(...nums)&#123;</span><br><span class="line">       <span class="keyword">return</span> nums.reduce(<span class="function"><span class="params">(p,n)</span>=&gt;</span>(p+n),<span class="number">0</span>)</span><br><span class="line">     &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight processing"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line">function <span class="built_in">log</span>(target)&#123;</span><br><span class="line">    <span class="keyword">const</span> desc = <span class="keyword">Object</span>.getOwnPropertyDescriptors(target.prototype);</span><br><span class="line">     </span><br><span class="line">    <span class="keyword">for</span>(<span class="keyword">const</span> <span class="built_in">key</span> of <span class="keyword">Object</span>.keys(desc))&#123;</span><br><span class="line">       <span class="keyword">if</span>(<span class="built_in">key</span> === <span class="string">'constructor'</span>)&#123;</span><br><span class="line">          <span class="keyword">continue</span>;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">       <span class="keyword">const</span> func = desc[<span class="built_in">key</span>].value;</span><br><span class="line"></span><br><span class="line">      <span class="keyword">if</span>(<span class="string">'function'</span>=== typeof func) &#123;</span><br><span class="line">         <span class="keyword">Object</span>.defineProperty(target.prototype,<span class="built_in">key</span>,&#123;</span><br><span class="line">          value(...args)&#123;</span><br><span class="line">           console.<span class="built_in">log</span>(<span class="string">'before'</span>+<span class="built_in">key</span>);</span><br><span class="line">           <span class="keyword">const</span> ret = func.apply(<span class="keyword">this</span>,args);</span><br><span class="line">           console.<span class="built_in">log</span>(<span class="string">'before'</span>+<span class="built_in">key</span>);</span><br><span class="line">           <span class="keyword">return</span> ret</span><br><span class="line">          &#125;</span><br><span class="line">             </span><br><span class="line">         &#125;)</span><br><span class="line">       &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight actionscript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">readonly</span><span class="params">(target,key,desc)</span></span>&#123;</span><br><span class="line">   desc.writable = <span class="literal">false</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight actionscript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">validate</span><span class="params">(target,key,desc)</span></span>&#123;</span><br><span class="line">    <span class="keyword">const</span> func = desc.value;</span><br><span class="line">    desc.value = <span class="function"><span class="keyword">function</span><span class="params">(<span class="rest_arg">...args</span>)</span></span>&#123;</span><br><span class="line">      <span class="keyword">for</span>(let num of args)&#123;</span><br><span class="line">          <span class="keyword">if</span>(<span class="string">'number'</span> === <span class="keyword">typeof</span> num)&#123;</span><br><span class="line">              <span class="keyword">throw</span> <span class="keyword">new</span> Error(`<span class="string">"$&#123;num&#125;"</span> <span class="keyword">is</span> not a number`);</span><br><span class="line">           &#125;</span><br><span class="line">       &#125;</span><br><span class="line">       <span class="keyword">return</span> func.apply(<span class="keyword">this</span>,args);</span><br><span class="line">   &#125;     </span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

      
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